Here's how memory in animals may improve treatments for Alzheimer's

Government and other scientists are proposing a new way to define Alzheimer's disease, basing it on biological signs, such as brain changes, rather than memory loss and other symptoms that are used now (April 10)
AP

New Indiana University research has shown that rodents do have the capacity for episodic memory replay. The discovery may someday lead to better treatments for Alzheimer's disease, researchers say.(Photo: Provided by Indiana University.)

Have you ever looked at your dog or cat and wondered whether it can remember that you recently rewarded or scolded them — and when that happened?

Indiana University neuroscientists have discovered what they say is the first evidence nonhuman animals can replay a stream of past events from memory — and even the sequence in which those events occurred.

The discovery of this type of episodic memory in rodents may someday help advance the development of new drugs to treat Alzheimer's disease, said Jonathon Crystal, a professor and director of the neurosciences program at IU-Bloomington.

"We did know that animals had episodic memory," Crystal said Thursday. "What this research showed is that they can remember a series of such events in the order in which they occurred."

Crystal said researchers ultimate goal is "to develop new models of memory that match up with the types of memory impaired in human diseases, such as Alzheimer's disease."

Professor Jonathon Crystal, director of the neuroscience program at Indiana University-Bloomington, led the study of episodic memory replay in animals, which is being published in the journal Current Biology.(Photo: Eric Rudd/Indiana University)

Most previous research on potential new treatments for Alzheimer's has examined how those drug compounds affect spatial memory, one of the easiest types to assess in animals, Crystal said.

But spatial memory — which allows you to form a "cognitive map" of your surroundings — isn't the type of memory most affected by patients with Alzheimer's disease.

However, "episodic memory replay" is key for such patients and the loss of it can make it hard to remember where you misplaced something, such as car keys, or make it difficult to recall an important event in your life or that of someone close to you. Such instances of memory loss can be heartbreaking and debilitating for a patient and his or her loved ones.

To study animals' episodic memory, Crystal and his researchers spent nearly a year working with 13 rats, which they trained to memorize a list of up to 12 different odors. Rats were placed inside an enclosure with stations with different odors and were rewarded when they identified the second-to-last odor or fourth-to-last odor in the list.

The team took steps in various tests to determine that the odors were being identified based on their position in the list, not by scent alone. That showed the rodents were able to recall the whole list in order.

Indiana University doctoral student Danielle Panoz-Brown is the first author of the study. "We're interested in episodic memory — and episodic memory replay — because it declines in Alzheimer's disease, and in aging in general," she said.(Photo: Provided by Indiana University.)

Crystal said we've long known about certain genetic markers that can make people more susceptible to getting Alzheimer's. Now new genetic tools are enabling scientists to experiment with rats with neurological conditions similar to that disease.

"If we want to eliminate Alzheimer's disease, we really need to make sure we're trying to protect the right type of memory," he said.

The next step, Crystal said, is to make a genetic model of Alzheimer's disease available for testing in rats to help develop new therapies that may someday lessen or eliminate the loss of episodic memory.

While Crystal isn't ready to say his research also proves that your cat or dog remembers better than you think, his research may add to new understanding — and respect — for the abilities of our animal friends.

"It does suggest that these type of capacities that we may have thought were only available in humans are much more widespread in the animal kingdom than we suspected," he said.